Photodetection device including interference element

ABSTRACT

A photodetection device comprises: an image sensor that includes first pixels, second pixels, third pixels, and fourth pixels; an interference element that includes first incident regions and second incident regions; and an optical system that causes light in a first wavelength band to be incident on the first incident regions and causes light in a second wavelength band different from the first wavelength band to be incident on the second incident regions. The interference element causes first interference of part of the light in the first wavelength band incident on two first incident regions that are included in the first incident regions. The interference element also causes second interference of part of the light in the second wavelength band incident on two second incident regions.

BACKGROUND

1. Technical Field

The present disclosure relates to a photodetection device including aninterference element.

2. Description of the Related Art

A device that measures the shape or a distance of an object with highaccuracy and in a noncontact manner by utilizing an interferencephenomenon of light is in practical use. Generally in such a device, thelight that has reflected off or passed through an object, which isreferred to as an object light, and the light that has reflected off areference surface, which is referred to as a reference light, are causedto interfere with each other. The generated interference light is imagedand observed. In a state where the degree of the flatness of thereference surface is sufficiently ensured, interference fringes of theinterference light occur according to the optical path length of theobject light. Difference in optical path length that corresponds to thewavelength of the light causes interference fringes of one period. Thus,the three-dimensional shape of a measured surface of the object can bedetermined from the pattern of the interference fringes.

The difference in optical path length equal to or larger than thewavelength of the light causes a repeat of interference fringes. Whenthe measured surface of the object is smooth, the difference in theoptical path length beyond the wavelength of the light can be estimatedby counting these interference fringes.

When the measured surface of the object includes a step beyond thewavelength, the interference fringes lack in the step portion andaccordingly, the difference in the optical path length is unable to bedetermined accurately. As a method of measuring the shape of an objectin such a case, two-wavelength interferometry is known. Thetwo-wavelength interferometry is described in for example, JapaneseUnexamined Patent Application Publication No. 10-221032 and Yeou-YenCheng and James C. Wyant: “Two-wavelength phase shiftinginterferometry”, Applied Optics, vol. 23, No. 24, pp. 4539 to 4543.

The two-wavelength interferometry uses lights with two wavelengths toperform interference measurement. Images of the interference fringesaccording to the lights with the respective wavelengths areindependently or simultaneously picked up and on the basis ofinformation on the interference fringes of both of the wavelengths, theshape of the measured surface of the object is determined. When the twowavelengths are referred to as λ₁ and λ₂, it is known that an effectivemeasurement wavelength λ_(eff) is obtained by the two-wavelengthinterferometry as expressed below.

$\lambda_{eff} = \frac{\lambda_{1}\lambda_{2}}{{\lambda_{1} - \lambda_{2}}}$

When for example, λ₂=1.1×λ₁, λ_(eff)=11×λ₁ and a step that is larger canbe accurately estimated.

SUMMARY

One non-limiting and exemplary embodiment provides a photodetectiondevice that has an optical part smaller in size and that is lesssusceptible to the influence of an ambient environment.

In one general aspect, the techniques disclosed here feature aphotodetection device that includes: an image sensor that includes firstpixels, second pixels, third pixels, and fourth pixels; an interferenceelement that includes first incident regions and second incidentregions; and an optical system that causes light in a first wavelengthband to be incident on the first incident regions and causes light in asecond wavelength band different from the first wavelength band to beincident on the second incident regions. The interference element causesfirst interference of part of the light in the first wavelength bandincident on two first incident regions that are included in the firstincident regions and that are adjacent to each other. The interferenceelement also guides resultant light of the first interference to any ofthe first pixels and guides another part of the light in the firstwavelength band incident on the two first incident regions to any of thesecond pixels, and causes second interference of part of the light inthe second wavelength band incident on two second incident regions thatare included in the second incident regions and that are adjacent toeach other, and guides resultant light of the second interference to anyof the third pixels and guides another part of the light in the secondwavelength band incident on the two second incident regions to any ofthe fourth pixels.

The present disclosure can achieve a photodetection device that has anoptical part smaller in size and that is less susceptible to theinfluence of an ambient environment.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a configuration of a photodetectiondevice according to a first embodiment of the present disclosure;

FIG. 2 illustrates a specific example of an optical system according tothe first embodiment of the present disclosure;

FIG. 3A illustrates another specific example of the optical systemaccording to the first embodiment of the present disclosure;

FIG. 3B illustrates another specific example of the optical systemaccording to the first embodiment of the present disclosure;

FIG. 3C illustrates another specific example of the optical systemaccording to the first embodiment of the present disclosure;

FIG. 3D illustrates another specific example of the optical systemaccording to the first embodiment of the present disclosure;

FIG. 3E illustrates still another specific example of the optical systemaccording to the first embodiment of the present disclosure;

FIG. 3F illustrates still another specific example of the optical systemaccording to the first embodiment of the present disclosure;

FIG. 4A illustrates an arrangement example of incident regions accordingto the first embodiment of the present disclosure;

FIG. 4B illustrates an arrangement example of the incident regionsaccording to the first embodiment of the present disclosure;

FIG. 4C illustrates an arrangement example of the incident regionsaccording to the first embodiment of the present disclosure;

FIG. 4D illustrates an arrangement example of the incident regionsaccording to the first embodiment of the present disclosure;

FIG. 4E illustrates an arrangement example of the incident regionsaccording to the first embodiment of the present disclosure;

FIG. 5A illustrates a specific example of an interference elementaccording to the first embodiment of the present disclosure;

FIG. 5B illustrates a specific example of the interference elementaccording to the first embodiment of the present disclosure;

FIG. 5C illustrates a specific example of the interference elementaccording to the first embodiment of the present disclosure;

FIG. 5D illustrates a specific example of the interference elementaccording to the first embodiment of the present disclosure;

FIG. 6A illustrates another specific example of the interference elementaccording to the first embodiment of the present disclosure;

FIG. 6B illustrates another specific example of the interference elementaccording to the first embodiment of the present disclosure;

FIG. 6C illustrates another specific example of the interference elementaccording to the first embodiment of the present disclosure;

FIG. 6D illustrates another specific example of the interference elementaccording to the first embodiment of the present disclosure;

FIG. 7A illustrates an arrangement example of pixels according to thefirst embodiment of the present disclosure;

FIG. 7B illustrates an arrangement example of the pixels according tothe first embodiment of the present disclosure;

FIG. 7C illustrates an arrangement example of the pixels according tothe first embodiment of the present disclosure;

FIG. 7D illustrates an arrangement example of the pixels according tothe first embodiment of the present disclosure;

FIG. 7E illustrates an arrangement example of the pixels according tothe first embodiment of the present disclosure;

FIG. 8 illustrates an output example of an optical intensity signalaccording to the first embodiment of the present disclosure;

FIG. 9 illustrates specific examples of computation units according tothe first embodiment of the present disclosure;

FIG. 10 is a schematic diagram of a configuration of a photodetectiondevice according to a second embodiment of the present disclosure;

FIG. 11 is a schematic diagram of a configuration of a photodetectiondevice according to a third embodiment of the present disclosure;

FIG. 12 illustrates a configuration of an interference element accordingto an example of the present disclosure;

FIG. 13 illustrates the relation between a phase difference of incidentlight and the intensities of interference light and transmitted lightaccording to an example of the present disclosure;

FIG. 14A illustrates the shape of a measured object (sample) accordingto a first example of the present disclosure;

FIG. 14B illustrates the shape of the measured object (sample) accordingto the first example of the present disclosure;

FIG. 15A illustrates the intensity of the light incident on each pixelof first pixels according to the first example of the presentdisclosure;

FIG. 15B illustrates the intensity of the light incident on each pixelof second pixels according to the first example of the presentdisclosure;

FIG. 15C illustrates the intensity of the light incident on each pixelof third pixels according to the first example of the presentdisclosure;

FIG. 15D illustrates the intensity of the light incident on each pixelof fourth pixels according to the first example of the presentdisclosure;

FIG. 16A illustrates distribution of phase difference absolute values ata center wavelength λ₁ according to the first example of the presentdisclosure;

FIG. 16B illustrates distribution of phase difference absolute values ata center wavelength λ₂ according to the first example of the presentdisclosure;

FIG. 17A illustrates distribution of phase difference values at thecenter wavelength λ₁ according to the first example of the presentdisclosure;

FIG. 17B illustrates distribution of phase difference values at thecenter wavelength λ₂ according to the first example of the presentdisclosure;

FIG. 18 illustrates distribution of phase difference values at anequivalent wavelength λ_(eff) according to the first example of thepresent disclosure;

FIG. 19 illustrates distribution of phase values at the equivalentwavelength λ_(eff) according to the first example of the presentdisclosure;

FIG. 20A illustrates distribution of phase values at the centerwavelength λ₁ according to the first example of the present disclosure;

FIG. 20B illustrates distribution of phase values at the centerwavelength λ₂ according to the first example of the present disclosure;

FIG. 21 illustrates a sample shape reconstructed at the equivalentwavelength λ_(eff) according to the first example of the presentdisclosure;

FIG. 22A illustrates a sample shape reconstructed at the centerwavelength λ₁ according to the first example of the present disclosure;

FIG. 22B illustrates a sample shape reconstructed at the centerwavelength λ₂ according to the first example of the present disclosure;

FIG. 23 illustrates the shape of a measured object (samples) accordingto a second example of the present disclosure;

FIG. 24A illustrates the relation between a step of a measured objectand the intensities of the interference light and the transmitted lightat the center wavelength λ₁ according to the second example of thepresent disclosure;

FIG. 24B illustrates the relation between the step of the measuredobject and the intensities of the interference light and the transmittedlight at the center wavelength λ₂ according to the second example of thepresent disclosure;

FIG. 25A illustrates the relation between the step of the measuredobject and the intensity of the interference light at the centerwavelength λ_(eff) according to the second example of the presentdisclosure;

FIG. 25B illustrates the relation between the step of the measuredobject and the intensity of the transmitted light at the centerwavelength λ_(eff) according to the second example of the presentdisclosure;

FIG. 26 illustrates an example of the relation between illuminationlight and bandpass filters; and

FIG. 27 illustrates another example of the relation between illuminationlight and bandpass filters.

DETAILED DESCRIPTION

<Underlying Knowledge Forming Basis of the Present Disclosure>

The present disclosure relates to a photodetection device that obtainsinformation on the shape or distance of an object as an image byutilizing an interference phenomenon of light. In particular, thepresent disclosure relates to a photodetection device that can measurevariations in step beyond a wavelength or in shape as an image with highaccuracy. The present inventors have reviewed the conventionalphotodetection devices that are disclosed in Japanese Unexamined PatentApplication Publication No. 10-221032 and Yeou-Yen Cheng and James C.Wyant: “Two-wavelength phase shifting interferometry”, Applied Optics,vol. 23, No. 24, pp. 4539 to 4543 in detail. The photodetection devicesdisclosed in the above-mentioned related art require a one-way mirrorfor causing interference light and occasionally need a camera tube or animage sensor for each wavelength. Thus, there may be a limitation indownsizing an optical system in a photodetection device. The presence ofan optical path in predetermined space may cause susceptibility tochange in or influence of an ambient environment, such as convection ofair or vibrations of the optical system.

In view of the above-described issues, the present inventors haveconceived a new photodetection device that has an optical part smallerin size and that is less susceptible to the influence of an ambientenvironment.

A photodetection device according to an aspect of the present disclosureincludes: an image sensor that includes first pixels, second pixels,third pixels, and fourth pixels; an interference element that includesfirst incident regions and second incident regions; and an opticalsystem that causes light in a first wavelength band to be incident onthe first incident regions and causes light in a second wavelength banddifferent from the first wavelength band to be incident on the secondincident regions. The interference element causes first interference ofpart of the light in the first wavelength band incident on two firstincident regions that are included in the first incident regions andthat are adjacent to each other, and guides resultant light of the firstinterference to any of the first pixels and guides another part of thelight in the first wavelength band incident on the two first incidentregions to any of the second pixels. The interference element alsocauses second interference of part of the light in the second wavelengthband incident on two second incident regions that are included in thesecond incident regions and that are adjacent to each other, and guidesresultant light of the second interference to any of the third pixelsand guides another part of the light in the second wavelength bandincident on the two second incident regions to any of the fourth pixels.

The “light in the first wavelength band” herein indicates light havingany wavelength included in the first wavelength band. The “light in thesecond wavelength band” indicates light having any wavelength includedin the second wavelength band. Thus, the light in the first wavelengthband and the light in the second wavelength band may each be light witha single wavelength or be light having a predetermined bandwidth.

The photodetection device may further include computation circuitry thatdetermines first phase difference information using optical intensityinformation detected at the first pixels and optical intensityinformation detected at the second pixels, and determines second phasedifference information using optical intensity information detected atthe third pixels and optical intensity information detected at thefourth pixels.

The computation circuitry may determine phase difference information atan equivalent wavelength of a first wavelength included in the firstwavelength band and a second wavelength included in the secondwavelength band using the first phase difference information and thesecond phase difference information.

The interference element may include optical coupling layers, and theoptical coupling layers may each include a waveguide layer that includesa diffraction grating.

The interference element may include a first light shielding regionpositioned between the two first incident regions and a second lightshielding region positioned between the two second incident regions. Theoptical coupling layers may include an optical coupling layer positionedat a location corresponding to the two first incident regions and thefirst light shielding region, or the two second incident regions and thesecond light shielding region. The second pixels may include two secondpixels positioned at a location corresponding to the two first incidentregions. The first pixels may include a first pixel positioned at alocation corresponding to the first light shielding region. The fourthpixels may include two fourth pixels positioned at a locationcorresponding to the two second incident regions. The third pixels mayinclude a third pixel positioned at a location corresponding to thesecond light shielding region.

The interference element may include a first optical propagation path, asecond optical propagation path, and a third optical propagation pathcoupled between the first optical propagation path and the secondoptical propagation path.

The first optical propagation path may include an incident portion onwhich light from one of the two first incident regions or one of the twosecond incident regions is incident, and an emission portion from whichpart of the light that is incident is emitted to any of the secondpixels or any of the fourth pixels. The second optical propagation pathmay include an incident portion on which light from the other of the twofirst incident regions or the other of the two second incident regionsis incident, and an emission portion from which part of the light thatis incident is emitted to any of the second pixels or any of the fourthpixels.

The interference element may further include a fourth opticalpropagation path, and the fourth optical propagation path may include anincident portion coupled to the third optical propagation path, and anemission portion from which the light incident from the incident portionis emitted to any of the first pixels or any of the third pixels.

The optical system may include a filter array that includes firstbandpass filters that selectively transmit the light in the firstwavelength band, and second bandpass filters that selectively transmitthe light in the second wavelength band.

The optical system may include a first bandpass filter that selectivelytransmits the light in the first wavelength band, a second bandpassfilter that selectively transmits the light in the second wavelengthband, and an array-shaped optical element that causes the light in thefirst wavelength band transmitted through the first bandpass filter tobe incident on the first incident regions, and causes the light in thesecond wavelength band transmitted through the second bandpass filter tobe incident on the second incident regions.

A photodetection device according to another aspect of the presentdisclosure includes: an image sensor that includes fifth pixels andsixth pixels; an interference element that includes fifth incidentregions; and illumination that emits light in a first wavelength bandand light in a second wavelength band different from the firstwavelength band. The interference element causes first interference ofpart of the light in the first wavelength band incident on two fifthincident regions that are included in the fifth incident regions andthat are adjacent to each other, and guides resultant light of the firstinterference to any of the fifth pixels and guides another part of thelight in the first wavelength band incident on the two fifth incidentregions to any of the sixth pixels. The interference element also causessecond interference of part of the light in the second wavelength bandincident on the two fifth incident regions, and guides resultant lightof the second interference to any of the fifth pixels and guides anotherpart of the light in the second wavelength band incident on the twofifth incident regions to any of the sixth pixels.

The illumination may emit the light in the first wavelength band and thelight in the second wavelength band simultaneously. The illumination mayemit the light in the first wavelength band and the light in the secondwavelength band in time division.

The first optical propagation path, the second optical propagation path,and the third optical propagation path may be configured with a photoniccrystal. The first optical propagation path, the second opticalpropagation path, the third optical propagation path, and the fourthoptical propagation path may be configured with a photonic crystal.

Embodiments of a photodetection device according to the presentdisclosure are described below with reference to the drawings.

Outline of First Embodiment

FIG. 1 is a schematic diagram that illustrates the outline of aconfiguration of a photodetection device according to a first embodimentof the present disclosure. The photodetection device includes an opticalsystem 101, an interference element 106, and an image sensor 109. Forconvenience in description, FIG. 1 depicts the interference element andthe image sensor in cross section. To facilitate understanding of thedrawings, three-axis directions x, y, and z based on a left-hand systemare also depicted in most of the drawings in and after FIG. 1. Specificexamples of constituents are described below.

The image sensor 109 includes first pixels 110, second pixels 111, thirdpixels 112, and fourth pixels 113.

Reflected light from the object whose three-dimensional shape ordistance is desired to be precisely measured is incident on the opticalsystem 101 as incident light.

The optical system 101 causes light in a first wavelength band 102 andlight in a second wavelength band 103 to be incident on the interferenceelement 106. The interference element 106 includes first incidentregions 104 and second incident regions 105. The optical system 101causes the light in the first wavelength band 102 to be incident mainlyon the first incident regions 104 of the interference element 106. Theoptical system 101 further causes the light in the second wavelengthband 103 to be incident mainly on the second incident regions 105.

The center wavelength of the light in the second wavelength band 103 isdifferent from that of the light in the first wavelength band 102. It ismore desirable, in terms of the possibility of precise determination ofa step on or the shape of an object, that the band of the light in thesecond wavelength band 103 and the band of the light in the firstwavelength band 102 have no overlapping. In addition, it is moredesirable, in terms of the possibility of increase in measurement rangewhile bringing the center wavelengths of the light in the two wavelengthbands closer to each other, that each of the bandwidths of the light inthe first wavelength band 102 and the light in the second wavelengthband 103 be 20 nm or less and it is still more desirable that each ofthe bandwidths be 5 nm or less.

It is sufficient for the first incident regions 104 and the secondincident regions 105 present in the interference element 106 to includeopenings that can transmit at least light and a physical structuretherefor may be omitted. The first incident regions 104 and the secondincident regions 105 may be physically the same as each other. The“first” incident regions and the “second” incident regions areseparately described herein since the properties of the light incidenton each incident region differ.

Part of the light incident from at least a pair of incident regionsadjacent to each other, which is included in the light incident on thefirst incident regions 104, is caused to interfere with each other inthe interference element 106 to be emitted to the side of the imagesensor 109 as interference light 107. Another part of the light incidentfrom the pair of incident regions is emitted directly to the side of theimage sensor 109 as transmitted light 108 without being caused tointerfere with each other. Similar to the light incident on the firstincident regions 104, the light incident on the second incident regions105 is also emitted to the side of the image sensor 109 as theinterference light 107 and the transmitted light 108.

It is desirable that the distance between the interference element 106and the image sensor 109 be short so as to efficiently cause theinterference light 107 and the transmitted light 108 to be incident onpixels of the image sensor 109, that is, so as to increase the couplingefficiency. The distance is desirably 100 μm or less and is moredesirably 10 μm or less.

The interference light 107 generated from the light in the firstwavelength band 102 is guided mainly to the first pixels 110 in theimage sensor 109 and the transmitted light 108 of the first wavelengthband 102 is guided mainly to the second pixels 111. Similarly, theinterference light 107 generated from the light in the second wavelengthband 103 and the transmitted light 108 of the second wavelength band 103are guided mainly to the third pixels 112 and the fourth pixels 113,respectively.

It is here sufficient for the first pixels 110, the second pixels 111,the third pixels 112, and the fourth pixels 113 to be photodetectors,such as photodiodes, and may be detectors with physically the samestructures. Herein the “first” to “fourth” pixels are separatelydescribed since the properties of the light incident on each pixeldiffer.

To process electric signals obtained from the image sensor 109, thephotodetection device further includes a first computation unit 114, asecond computation unit 115, and a third computation unit 118.Information on the intensity of the light incident on the first pixels110 and the second pixels 111 is input to the first computation unit 114as electric signals. On the basis of the input signals, the firstcomputation unit 114 calculates and outputs first phase differenceinformation 116. The first phase difference information 116 correspondsto phase difference information with respect to the center wavelength inthe first wavelength band, that is, λ₁ of a related-art example.

Similarly, information on the intensity of the light incident on thethird pixels 112 and the fourth pixels 113 is input to the secondcomputation unit 115 as electric signals. On the basis of the inputsignals, the second computation unit 115 calculates and outputs secondphase difference information 117. The second phase differenceinformation 117 corresponds to phase difference information with respectto the center wavelength in the second wavelength band, that is, λ₂ of arelated-art example.

On the basis of the first phase difference information 116 and thesecond phase difference information 117, the third computation unit 118calculates and outputs equivalent phase difference information 119, thatis, phase difference information with respect to λ_(eff) of arelated-art example.

Such a configuration can achieve a photodetection device that has anoptical part smaller in size, is less susceptible to the influence of anambient environment, and can correctly measure the shape of an objecteven when the object includes a step beyond the wavelength of light.

<Specific Configuration Examples of Optical System>

Specific configuration examples of the optical system 101 are describednext with reference to FIG. 2 and FIGS. 3A to 3F.

FIG. 2 illustrates a filter array as part of the optical system 101. Thefilter array includes first bandpass filters 201 and second bandpassfilters 202 arranged so as to be close to the light incident side of theinterference element 106. The first bandpass filters 201 have wavelengthcharacteristics of transmitting light in the first wavelength band andare arranged so as to be adjacent to the first incident regions 104. Thesecond bandpass filters 202 have wavelength characteristics oftransmitting light in the second wavelength band and are arranged so asto be adjacent to the second incident regions 105. The bandpass filteris manufactured by for example, forming a dielectric multilayered filmor a film with a pigment. In the optical system 101, the regions inwhich no bandpass filters are present are desirably light shieldingregions.

FIGS. 3A to 3D illustrate an example in which the optical system 101includes a bandpass filter and an array-shaped optical element arrangednear a pupil region. The optical system 101 includes an aperture 306having the pupil region, a filter array 307, a lens 304, and anarray-shaped optical element 305. FIG. 3A schematically illustrates aconfiguration of the optical system 101 and FIG. 3B illustrates a planarconfiguration of the filter array 307. FIG. 3C is a schematicperspective view of the array-shaped optical element 305 and FIG. 3Dschematically illustrates light that passes through the optical system101 to be incident on the interference element 106.

As illustrated in FIGS. 3A and 3B, the pupil region of the aperture 306is divided into a region D1 and a region D2 by a plane that includes anoptical axis V of the optical system 101 and expands in a horizontaldirection. The filter array 307 includes a second bandpass filter 303arranged in the region D1 and a first bandpass filter 302 arranged inthe region D2.

The incident light that passes through the first optical region D1 andthe second optical region D2 is focused through the lens 304 to beincident on the array-shaped optical element 305. The array-shapedoptical element 305 is for example, a lenticular lens where cylindricallenses that each extend in the x direction are arranged in the ydirection. The array-shaped optical element 305 causes light in thefirst wavelength band, which passes through the first bandpass filter302, to be incident on the first incident regions 104 and causes lightin the second wavelength band, which passes through the second bandpassfilter 303, to be incident on the second incident regions 105. Toincrease the incidence efficiency on the first incident regions 104 andthe second incident regions 105, a microlens array 308 may be arrangedon a surface of the interference element 106.

As described below, the filter array 307 and the array-shaped opticalelement 305 may have shapes illustrated in FIGS. 3E and 3F,respectively.

The transmission wavelength characteristics of the first bandpass filter302 and the second bandpass filter 303 are similar to the transmissionwavelength characteristics of the first bandpass filter 201 and thesecond bandpass filter 202 respectively, which are described withreference to FIG. 2. What differs is the largeness in size of eachbandpass filter and when the size of a bandpass filter is large, it isadvantageous in that the manufacturing of bandpass filters isfacilitated. Replacing a bandpass filter only with a bandpass filterwith a different center wavelength can vary the measurable range.

In the examples of FIG. 2 and FIGS. 3A to 3F, when the wavelengthbandwidth of the incident light is relatively wide like a case where forexample, a halogen lamp or a white LED light source is used, light withtwo wavelength bandwidths can be suitably extracted through bandpassfilters (see FIG. 26). When each of the two wavelength bands included inthe incident light originally has a bandwidth of a degree the same as orsmaller than the transmission wavelength band of each bandpass filterlike two laser light sources for example, the transmission bandwidth ofeach bandpass filter is not necessarily required to be narrow. In such acase, the transmission bandwidth of each bandpass filter may berelatively wide as long as light in two wavelength bands can beseparated from each other. Instead of bandpass filters, a low-passfilter that transmits light in the first wavelength band and a high-passfilter that transmits light in the second wavelength band may be used(see FIG. 27). An optical filter with a wide transmission bandwidth canbe easily manufactured.

<Arrangement Examples of Incident Regions>

While FIG. 1 illustrates the interference element 106 as across-sectional view, arrangement examples of the incident regions inthe interference element 106 viewed from the front, that is, the lightincident side are described using FIGS. 4A to 4E.

FIG. 4A illustrates an example in which the first incident regions 104and the second incident regions 105 are arranged together in a column.Use of such a configuration enables a one-dimensional shape or distanceinformation of a measured object to be measured with a linear imagesensor.

FIG. 4B illustrates an example in which the first incident regions 104and the second incident regions 105 are arranged in respective columns.Use of such a configuration has an advantage that when the interferenceelement is manufactured with a grating, the manufacturing is facilitatedas described below.

FIG. 4C illustrates two-dimensional expansion of the arrangement of theincident regions illustrated in FIG. 4B. According to the arrangement, atwo-dimensional shape or distance information of a measured object canbe measured as an image.

FIG. 4D illustrates another two-dimensional arrangement example of theincident regions. The first incident regions 104 and the second incidentregions 105 are arranged alternately in two columns each. When in thepresent example, bandpass filters are arranged so as to be close to eachincident region, the width of each bandpass filter can be ensured to bewide, that is, can be caused to be a width corresponding to two columnsof the incident regions and accordingly, it is advantageous in that themanufacturing of the bandpass filters is facilitated.

FIG. 4E illustrates still another two-dimensional arrangement example ofthe incident regions. The first incident regions 104 and the secondincident regions 105 are arranged in units of four columns and fourrows, that is, in units of eight regions in total. Also in this case,the width of each bandpass filter can be ensured to be wide, that is,can be caused to be a width corresponding to four columns andaccordingly, it is advantageous in that the manufacturing of bandpassfilters is facilitated.

The shape of an incident region viewed from the front is not necessarilyrequired to be a square and may be a circle, a rectangle, or the like.

When as illustrated in FIG. 2, a filter array arranged so as to be closeto the light incident side of the interference element 106 is used asthe optical system 101, a filter array may be used, where the firstbandpass filters 201 and the second bandpass filters 202 are arrangedaccording to the arrangement of the first incident regions 104 and thesecond incident regions 105 as illustrated in FIGS. 4A to 4E.

As described with reference to FIGS. 3A to 3D, when the optical system101 includes bandpass filters arranged near a pupil region and anarray-shaped optical element, the configuration that is described belowis employed.

When as illustrated in FIG. 4A, the first incident regions 104 and thesecond incident regions 105 are one-dimensionally arranged in the ydirection in the interference element 106, the filter array 307 wherethe second bandpass filter 303 and the first bandpass filter 302 arearranged in the y direction as illustrated in FIG. 3A and thearray-shaped optical element (lenticular lens) 305 where cylindricallenses extending in the x direction are arranged in the y direction asillustrated in FIG. 3C are used. In this case, since the first incidentregions 104 and the second incident regions 105 of the interferenceelement 106 are one-dimensionally arranged, the length of thearray-shaped optical element 305 in the x direction may be a length thatcorresponds to one pixel.

When as illustrated in FIGS. 4B to 4D, the interference element 106where the first incident regions 104 and the second incident regions 105are arranged in different columns is used, a filter array where thesecond bandpass filters 303 and the first bandpass filters 302 arearranged in the x direction and a lenticular lens where cylindricallenses extending in the y direction are arranged in the x direction isused. In other words, what is obtained by exchanging the respectivearrangements in the x direction and the y direction of the filter array307 illustrated in FIG. 3A and the array-shaped optical element 305illustrated in FIG. 3C is used. When as illustrated in FIGS. 4B and 4C,the interference element 106 where the first incident regions 104 in onecolumn and the second incident regions 105 in one column are arranged asa unit is used, each cylindrical lens of the lenticular lens has a widththat corresponds to two pixels. When as illustrated in FIG. 4D, theinterference element 106 where the first incident regions 104 in twocolumns and the second incident regions 105 in two columns are arrangedas a unit is used, each cylindrical lens of the lenticular lens has awidth that corresponds to four pixels.

When as illustrated in FIG. 4E, the interference element 106 where thefirst incident regions 104 and the second incident regions 105 arearranged in a check pattern is used, the filter array 307 illustrated inFIG. 3E is used. The pupil region of the aperture 306 is divided intoregions D1 to D4 by two planes that include an optical axis V of theoptical system 101 and that are orthogonal to each other. The filterarray 307 includes the second bandpass filters 303 arranged in theregions D2 and D4 and the first bandpass filters 302 arranged in theregions D1 and D3. As illustrated in FIG. 3F, a microlens array wheremicrolenses M are arranged in the x direction and the y direction isused for the array-shaped optical element 305. Each microlens Mcorresponds to the size of 16 pixels, which are arranged in four columnsand four rows in the x direction and the y direction, respectively.

<Specific Configuration Example of Interference Element>

A specific configuration example of the interference element 106 and itsarrangement relation to pixels are described next with reference toFIGS. 5A to 5D and FIGS. 6A to 6D.

FIGS. 5A to 5D illustrate examples of cases where optical couplinglayers are used for the interference element 106 as cross-sectionalviews.

Each of optical coupling layers 502 includes a waveguide layer 504 wherea grating 503 is formed. Each waveguide layer 504 is positioned at alocation corresponding to two incident regions that are included in thefirst incident regions 104 and that are adjacent to each other or to twoincident regions that are included in the second incident regions 105and that are adjacent to each other. A base of the interference element106 may be formed of SiO₂ for example. The waveguide layer 504 is alayer with a refractive index that is higher than that of the base andmay be formed of Ta₂O₅ for example. The waveguide layer 504 is notlimited to a single layer and may be made up of layers while layers thateach have a low refractive index are sandwiched therebetween.

On an interface of the waveguide layer 504 on at least the incidentside, the gratings 503 are positioned with predetermined pitches. Thegrating 503 is a straight grating and the directions of the latticevectors of the grating 503 are parallel to the vertical direction on theplanes of FIGS. 5A to 5D within a plane of the optical coupling layer502.

On the light incident side of the interference element 106, lightshielding regions 501 are arranged in the regions that are neither thefirst incident regions 104 nor the second incident regions 105. That is,light shielding regions are positioned between two incident regions thatare included in the first incident regions 104 and that are adjacent toeach other and between two incident regions that are included in thesecond incident regions 105 and that are adjacent to each other. Thelight shielding region 501 is formed of a metal material withreflectivity, such as Al, Ag, or Au, and is thick enough to block lightin the first and second wavelength bands sufficiently.

An optical path of light incident on the first incident regions 104 isdescribed below using FIG. 5A. When the pitches of the gratings 503 areset so as to couple light in the first wavelength band, part of thelight incident on two incident regions 104 a and 104 b, which areincluded in the first incident regions and that are adjacent to eachother, is incident into the waveguide layer 504 to propagate aswaveguide light 506 a and waveguide light 506 b, respectively. Thewaveguide light 506 a and the waveguide light 506 b interfere with eachother in the waveguide layer 504 and is emitted as interference light107 a from the waveguide layer 504 to the side of the image sensor 109to be incident on a pixel 110 a, which is one of the first pixels 110.The waveguide light 506 a and the waveguide light 506 b propagate fromthe incident regions 104 a and 104 b, respectively, which are adjacentto each other and that form a pair. The intensity of the interferencelight 107 depends on a phase difference of light incident on the firstincident regions 104. Another part of the light incident on the incidentregions 104 a and 104 b is emitted as transmitted light 108 a andtransmitted light 108 b to the side of the image sensor 109 withoutbecoming waveguide light, and is incident on pixels 111 a and 111 bincluded in the second pixels 111. Accordingly, a phase difference oflights in the first wavelength band incident on the incident regions 104a and 104 b can be determined by detecting the intensities of the lightsincident on the pixels 110 a, 111 a, and 111 b.

As illustrated in FIG. 5A, an optical path of light incident on thesecond incident regions 105 can be explained in a similar manner to theabove. The reasons why a phase difference of the lights incident on apair of incident regions that are included in the second incidentregions 105 and that are adjacent to each other can be determined fromthe intensities of the lights incident on the third pixels 112 and theintensities of the lights incident on the fourth pixels 113 are similarto those of the case regarding the first incident regions.

FIG. 5A illustrates a cross-sectional configuration of the opticalcoupling layers 502 in the interference element 106 where the firstincident regions 104 and the second incident regions 105 areone-dimensionally arranged as illustrated in FIG. 4A. In thisconfiguration, since both the first incident regions 104 and the secondincident regions 105 are present in the directions of the latticevectors of the grating, the optical coupling layers 502 may be separatedto each other. The optical coupling layers 502 may be separated inboundaries between the first incident regions 104 and the secondincident regions 105 by media that each have a refractive index lowerthan that of the waveguide layer 504. According to this manner, nomutual interference occurs between the light in the first wavelengthband and the light in the second wavelength band separated through thebandpass filters and thus, a phase difference of lights in the firstwavelength band and a phase difference of lights in the secondwavelength band can be detected independently.

FIGS. 5B and 5C illustrate cross-sectional configurations of the opticalcoupling layer 502 in cases where the first incident regions 104 and thesecond incident regions 105 are arranged in different columns asillustrated in FIGS. 4B, 4C, and 4D. FIG. 5B is a cross-sectional viewtaken when the interference element 106 is cut in a column of the firstincident regions 104. FIG. 5C is a cross-sectional view taken when theinterference element 106 is cut in a column of the second incidentregions 105. Since in this configuration, only the first incidentregions 104 or the second incident regions 105 are present in thedirections of the lattice vectors of the grating, a phase difference oflights in the first wavelength band and a phase difference of lights inthe second wavelength band can be independently detected withoutseparating the optical coupling layer. The configuration where theoptical coupling layer 502 is not separated makes the manufacturing theoptical coupling layer 502 easier.

FIG. 5D illustrates a cross-sectional configuration of the opticalcoupling layers 502 in the case where the first incident regions 104 andthe second incident regions 105 are arranged in a check pattern asillustrated in FIG. 4E. Since in this configuration, similar to FIG. 5A,both the first incident regions 104 and the second incident regions 105are present in the directions of the lattice vectors of the gratings,the optical coupling layers may be separated to each other. The opticalcoupling layers may be separated in boundaries between the firstincident regions 104 and the second incident regions 105. Pixelsimmediately under the portions where the optical coupling layers areseparated may be referred to as unused pixels 505 and excluded incalculating phase difference information.

<Another Example of Specific Configuration of Interference Element>

FIGS. 6A to 6D illustrate examples of cases where a photonic crystal isused for the interference element 106 as cross-sectional views.

A photonic crystal 601 is used so as to form an optical propagationpath. The optical propagation path includes at least a first opticalpropagation path 602 and a second optical propagation path 603, and athird optical propagation path 604 that couples the first opticalpropagation path 602 and the second optical propagation path 603. Anincident portion of the first optical propagation path 602 is arrangedat a position different from the position of an incident portion of thesecond optical propagation path 603. An emission portion of the firstoptical propagation path 602 is arranged at a position different fromthe position of an emission portion of the second optical propagationpath 603. The optical propagation path illustrated in FIG. 6A furtherincludes a fourth optical propagation path 605. The fourth opticalpropagation path 605 is coupled to the third optical propagation path604 and allows light incident from the third optical propagation path604 to propagate. When the interference light and the transmitted lightare separately detected in a similar manner to the case where theoptical coupling layers 502 configure the interference element, it isdesirable for the optical propagation path to include the fourth opticalpropagation path 605. The intensities of the emission light of the firstoptical propagation path 602 and the emission light of the secondoptical propagation path 603 vary, depending on a phase difference ofthe lights incident on the first optical propagation path 602 and thesecond optical propagation path 603. Thus, phase difference informationcan be determined even in a configuration where the fourth opticalpropagation path 605 is not present.

The photonic crystal 601 is configured so as to have a periodicarrangement of for example, cavities, regions different in refractiveindex, dielectric posts, or the like, and an optical propagation path isformed by removing part of the periodic arrangement. The positions ofthe incident portions of the first optical propagation path 602 and thesecond optical propagation path 603 respectively correspond to twoincident regions that are included in the first incident regions 104 andthat are adjacent to each other. That is, the first optical propagationpath 602 and the second optical propagation path 603 are respectivelycoupled to two incident regions that are included in the first incidentregions 104 and that are adjacent to each other. The first incidentregions 104 include pairs of two incident regions that are adjacent toeach other as described above. The second incident regions 105 alsoinclude pairs of two incident regions that are adjacent to each other asdescribed above. Pairs of the first and second optical propagation pathsare arranged at a location corresponding to the pairs of the incidentregions in a manner similar to the above. The third optical propagationpath that couples the first optical propagation path and the secondoptical propagation path, and the fourth optical propagation pathcoupled to the third optical propagation path are arranged at a locationcorresponding to each pair of the first and second optical propagationpaths.

Each of the emission portions of the first optical propagation path 602and the second optical propagation path 603 is disposed so as to beadjacent to corresponding one of the second pixels 111. The emissionportion of the fourth optical propagation path 605 is disposed so as tobe adjacent to corresponding one of the first pixels 110. Similarly,each of the emission portions of the first and second opticalpropagation paths corresponding to the other first incident regions 104is disposed so as to be adjacent to corresponding one of the secondpixels 111. Each of the emission portions of the fourth opticalpropagation paths corresponding to the other first incident regions 104is disposed so as to be adjacent to corresponding one of the firstpixels 110. Similarly, each of the emission portions of the first andsecond optical propagation paths corresponding to the second incidentregions 105 is disposed so as to be adjacent to corresponding one of thefourth pixels 113. Each of the emission portions of the fourth opticalpropagation paths corresponding to the second incident regions 105 isdisposed so as to be adjacent to corresponding one of the third pixels112.

Since in this configuration, both the first incident regions 104 and thesecond incident regions 105 are present in the direction in which thethird optical propagation paths 604 extend, the third opticalpropagation paths 604 may be separated by leaving a dielectric post ineach boundary between the first incident regions 104 and the secondincident regions 105. According to this manner, no mutual interferenceof lights in the first and second wavelength bands separated through thebandpass filters occurs and thus, a phase difference of lights in thefirst wavelength band and a phase difference of lights in the secondwavelength band can be independently detected.

Such a configuration causes part of the light incident from a pair ofincident regions that are included in the first incident regions 104 andthe second incident regions 105 and that are adjacent to each other tointerfere in the third optical propagation path to be emitted from theinterference element 106 as the interference light 107. The state of theinterference of the light in the third optical propagation path changes,depending on a phase difference of lights incident from a pair ofincident regions adjacent to each other. Another part of the lightsincident from the incident regions is emitted from the interferenceelement 106 as the transmitted light 108. When the intensities of theinterference light 107 and the transmitted light 108 are detected at thepixels of the image sensor 109, similar to the case where the opticalcoupling layers 502 configure the interference element 106, the phasedifference information on lights can be determined.

FIG. 6A illustrates a cross-sectional configuration of the interferenceelement 106 where the first incident regions 104 and the second incidentregions 105 are one-dimensionally arranged as illustrated in FIG. 4A.

FIGS. 6B and 6C illustrate cross-sectional configurations of theinterference element 106 in the cases where the first incident regions104 and the second incident regions 105 are arranged in differentcolumns as illustrated in FIGS. 4B, 4C, and 4D. Since in theseconfigurations, only the first incident regions 104 or the secondincident regions 105 are present in the direction in which the thirdoptical propagation paths 604 extend, a phase difference of lights inthe first wavelength band and a phase difference of lights in the secondwavelength band can be independently detected without separating thethird optical propagation paths 604.

FIG. 6D illustrates a cross-sectional configuration of the interferenceelement 106 in the case where the first incident regions 104 and thesecond incident regions 105 are arranged in a check pattern asillustrated in FIG. 4E. FIGS. 6A and 6D illustrate configurations wherethe first incident regions 104 and the second incident regions 105 arearranged in the same column. In such configurations, when opticalpropagation paths are separated according to each wavelength band of theincidence from an incident region as illustrated in FIGS. 6A and 6D, aphase difference of lights in the first wavelength band and a phasedifference of lights in the second wavelength band can be independentlydetected.

<Pixel Arrangement of Image Sensor>

While FIG. 1, FIGS. 5A to 5D, and FIGS. 6A to 6D illustrate the imagesensor 109 as cross-sectional views, arrangement examples of the pixelsin the image sensor 109 viewed from the front, that is, the lightincident side are described using FIGS. 7A to 7E.

FIGS. 7A to 7E each illustrate an arrangement example of the pixels in acase where the first incident regions 104 and the second incidentregions 105 are arranged as illustrated in FIGS. 4A to 4E. The pixelsare arranged so that the interference light 107 of the lights incidenton the first incident regions 104 is incident on any pixel included inthe first pixels 110, the transmitted light 108 of the light incident onthe first incident regions 104 is incident on any pixel included in thesecond pixels 111, the interference light 107 of the lights incident onthe second incident regions 105 is incident on any pixel included in thethird pixels 112, and the transmitted light 108 of the light incident onthe second incident regions 105 is incident on any pixel included in thefourth pixels 113. It is more desirable that the position of eachincident region and the position of each pixel be in close agreementwith each other. In other words, it is desirable that those positionshave almost no deviation because unnecessary components of crosstalk toeach pixel can be reduced.

<Configuration Examples of Computation Units>

Using FIGS. 8 and 9, flow of signals from the image sensor 109 in thephotodetection device illustrated in FIG. 1 and configuration examplesof the computation units are described.

As illustrated in FIG. 8, the incident regions, the light shieldingregions, and signals output from each pixel of the image sensor aredefined. Each signal is output according to the intensity of lightincident on each corresponding pixel.

The incident regions and the light shielding regions are referred to asdescribed below. The nth incident region that belongs to the mthincident regions is denoted as A_(mn). The pair of A_(m1) and A_(m2) andthe pair of A_(m3) and A_(m4) each form a pair of incident regions,which are included in the mth incident regions and that are adjacent toeach other. The nth light shielding region present between the incidentregions or a region that is no incident region is denoted as S_(0n).

Signals are referred to as described below. A signal of the transmittedlight from a pixel immediately under the incident region A_(mn) or alight shielding region S_(mn) is denoted as t_(mn). A signal of theinterference light from a pixel immediately under the incident regionA_(mn) or the light shielding region S_(mn) is denoted as i_(mn).

As illustrated in FIG. 9, the first computation unit 114 receivessignals t₁₁, i₀₁, t₁₂, t₁₃, i₀₃, and t₁₄ and outputs first phasedifference information p₁₁, p₀₁, p₁₂, p₁₃, p₀₃, p₁₄. The secondcomputation unit 115 receives signals t₂₁, i₀₂, t₂₂, t₂₃, i₀₄, and t₂₄and outputs second phase difference information p₂₁, p₀₂, p₂₂, p₂₃, p₀₄,p₂₄. The third computation unit 118 receives the first phase differenceinformation p₁₁, p₀₁, p₁₂, p₁₃, p₀₃, p₁₄ and the second phase differenceinformation p₂₁, p₀₂, p₂₂, p₂₃, p₀₄, p₂₄ and outputs equivalent phasedifference information E₁₁, E₀₁, E₁₂, E₂₁, E₀₂, E₂₂, E₁₃, E₀₃, E₁₄, E₂₃,E₀₄, E₂₄. The pieces of the information described above may berepresented as electric signals or may be information held in memory ofa computer or the like. The first computation unit 114, the secondcomputation unit 115, and the third computation unit 118 are an exampleof the computation circuitry.

The first phase difference information 116 is phase differenceinformation with respect to the center wavelength of the firstwavelength band, that is, λ₁ of a related-art example, and the secondphase difference information 117 is phase difference information withrespect to the center wavelength of the second wavelength band, that is,λ₂ of a related-art example. Phase difference information of lightsseparated from the position of the incident region A_(mn) or the lightshielding region S_(mn) by an adjacent distance d_(adj), that is, adistance between a pair of incident regions adjacent to each other isdenoted as p_(mn).

Equivalent phase difference information 119 is phase differenceinformation with reference to an equivalent wavelength, that is, λ_(eff)of a related-art example. Equivalent phase difference information oflights separated from the position of the incident region A_(mn) or thelight shielding region S_(mn) by an adjacent distance d_(adj), that is,a distance between a pair of incident regions adjacent to each other isdenoted as E_(mn).

The first computation unit 114 determines the phase differenceinformation p₁₁, p₀₁, p₁₂, p₁₃, p₀₃, p₁₄ on each incident region orlight shielding region through computation based on the signals t₁₁,i₀₁, t₁₂, t₁₃, i₀₃, and t₁₄ that are output after causing lights in thefirst wavelength band to interfere with each other or to pass. Thedetermination is enabled by determining the relation between the opticalintensity of the interference light 107 or the transmitted light 108 andthe phase difference on the incident region or the light shieldingregion present immediately above through an experiment in advance,causing the relation to be held in memory as a table or a computationalexpression, and using the held table or computational expression. Forexample, two first wavelength lights whose phase difference is known arecaused to be incident on two incident regions that are included in thefirst incident regions and that are adjacent to each other, and theintensity of the interference light or the transmitted light ismeasured. The relation between a phase difference and an opticalintensity can be determined empirically by varying the phase differenceof the two first wavelength lights and repeating the measurement of theintensity of the interference light or transmitted light. The distancethat corresponds to the phase difference can be determined throughcomputation based on the wavelengths of the used lights.

Similar to the first computation unit 114, the second computation unit115 determines the phase difference information p₂₁, p₀₂, p₂₂, p₂₃, p₀₄,p₂₄ on each incident region or light shielding region throughcomputation based on the signals t₂₁, i₀₂, t₂₂, t₂₃, i₀₄, and t₂₄ thatare output after causing lights in the second wavelength band tointerfere with each other or to pass.

The third computation unit 118 determines the equivalent phasedifference information E₁₁, E₀₁, E₁₂, E₂₁, E₀₂, E₂₂, E₁₃, E₀₃, E₁₄, E₂₃,E₀₄, E₂₄ using the first phase difference information p₁₁, p₀₁, p₁₂,p₁₃, p₀₃, p₁₄ related to light in the first wavelength band and thesecond phase difference information p₂₁, p₀₂, p₂₂, p₂₃, p₀₄, p₂₄ relatedto light in the second wavelength band. The equivalent phase differenceinformation can be determined by known techniques described in JapaneseUnexamined Patent Application Publication No. 10-221032 or Yeou-YenCheng and James C. Wyant: “Two-wavelength phase shiftinginterferometry”, Applied Optics, vol. 23, No. 24, pp. 4539 to 4543.

The phase difference information is not necessarily required to bedetermined by being caused to correspond to all the incident regions orthe light shielding regions, that is, to all the pixels of the imagesensor. The phase difference information may be determined from averagephase difference information of regions across incident regions or alight shielding region, which are for example, the regions A₁₁, S₀₁, andA₁₂ in FIG. 8.

As the phase difference information, it may be unnecessary to determinean actual phase difference value and it is sufficient when the phasedifference information is a value related to a phase difference oflights incident between certain regions in the interference element.

The shape of a measured object is determined on the basis of the phasedifference information.

<Advantages of First Embodiment>

According to the present embodiment, interference light is caused insidethe interference element 106 arranged so as to be close to the imagesensor 109 and thus, a large optical component, such as a one-way mirroror a reference mirror is unnecessary and a photodetection device smallerin size than a conventional photodetection device can be achieved. Sincethe bandpass filters arranged immediately above the interference elementor near the pupil region separate two wavelength bands, it isunnecessary to use a plurality of camera tubes or image sensors and theoptical part of the photodetection device may be made smaller in sizethan that of a conventional photodetection device. Also, since lights ina plurality of wavelength bands are used for measurement, the shape ofan object can be correctly measured even when the object includes a stepbeyond the wavelength of light. Further, since it is unnecessary toroute an optical path in air for causing an interference phenomenon,precise measurement results can be obtained, which are less susceptibleto the influence of an ambient environment, such as air convection orvibrations.

Second Embodiment

In the first embodiment, lights in two wavelength bands with differentcenter wavelengths are obtained by causing incident light to passthrough bandpass filters. According to the first embodiment, even whenthe incident light has a wide wavelength band of some degree, such as ahalogen lamp or a white LED light, use of a bandpass filter with atransmission band narrower than the wavelength band of the incidentlight enables lights in two wavelength bands to be suitably obtained.

In contrast, when lights in two wavelength bands as incident light eachhave a wavelength spectrum with a width of the same degree as that ofthe transmission wavelength band of a bandpass filter originally, anembodiment of a configuration without a bandpass filter is alsoconceivable. Described below is the embodiment. Examples of such a lightsource include a laser light source.

FIG. 10 is a diagram for describing a structure according to a secondembodiment of the present disclosure.

Illumination 1001 irradiates a measured object with light in a first orsecond wavelength band. A wavelength band switch 1002 controls theillumination 1001 so that the illumination 1001 switches lights in thetwo wavelength bands with different center wavelengths in time divisionto emit the light.

For example, the illumination 1001 may include a wavelength tunablelaser light source and the wavelength band switch 1002 may includecircuitry that switches the wavelength of the wavelength tunable laserlight source. The illumination 1001 may include two laser light sourceswith different emission wavelength bands and the wavelength band switch1002 may include circuitry that switches emission or no emission fromthe two laser light sources alternately. The illumination 1001 mayinclude a light source with a relatively wide wavelength band andbandpass filters and the wavelength band switch 1002 may include amechanism that alternately switches the bandpass filters arranged on anoptical path from the light source.

The light that has passed through or reflected off the measured objectis incident on an optical system 1003 as the incident light. The opticalsystem 1003 causes light in a first or second wavelength band 1004 to beincident on fifth incident regions 1005 without dividing the wavelengthbands of the incident light in terms of space. The procedure in whichinterference light 107 and transmitted light 108 are caused in aninterference element 106 is similar to that in the first embodiment. Theprocedure in which the interference light 107 and the transmitted light108 are incident on fifth pixels 1006 and sixth pixels 1007 of an imagesensor 109 is also similar to that in the first embodiment. What isdifferent from the first embodiment is that light in the first andsecond wavelength bands can be incident on any incident region and anypixel.

Optical intensity signals output from the fifth pixels 1006 and thesixth pixels 1007 are input to a fourth computation unit 1009. On thebasis of the input signals, the fourth computation unit 1009 calculatesand outputs first phase difference information 116 and second phasedifference information 117. The procedure in which phase differenceinformation is determined from optical intensity signals is similar tothat in the first embodiment. What is different is that, on the basis ofa synchronization signal 1008 from the wavelength band switch 1002, thefirst phase difference information 116 is determined using opticalintensity signals at a timing of the irradiation with light in the firstwavelength band and the second phase difference information 117 isdetermined using optical intensity signals at a timing of theirradiation with light in the second wavelength band.

Similar to the first embodiment, a third computation unit 118 calculatesand outputs equivalent phase difference information 119 based on thefirst phase difference information 116 and the second phase differenceinformation 117. The third computation unit 118 and the fourthcomputation unit 1009 are an example of the computation circuitry.

Since such a configuration needs no use of a bandpass filter for anoptical system, a photodetection device that is still simpler inconfiguration can be achieved.

Third Embodiment

The second embodiment describes a configuration where illuminationlights in two wavelength bands with different center wavelengths areswitched in time division to be emitted. A third embodiment describes aconfiguration where simultaneous irradiation with illumination lights intwo wavelength bands is performed.

FIG. 11 is a diagram for describing a configuration according to thethird embodiment of the present disclosure.

A measured object is simultaneously irradiated with illumination in afirst wavelength band 1101 and illumination in a second wavelength band1102. The two illuminations have emission wavelength bands withdifferent center wavelengths. It is more desirable that the emission ofthe two illuminations is performed using for example, a beam splitterwhile an optical axis and the emission direction are caused to be thesame.

The light that has passed through or reflected off the measured objectis incident on an optical system 1003 as the incident light. The opticalsystem 1003 causes light in first and second wavelength bands 1103 to beincident on fifth incident regions 1005 without separating thewavelength bands of the incident light in terms of space. That the lightin the first and second wavelength bands can be incident on any incidentregion and any pixel of the fifth incident regions 1005 is similar tothe second embodiment.

Interference light 107 is incident on fifth pixels 1006 and transmittedlight 108 is incident on sixth pixels 1007. Since the interference light107 and the transmitted light 108 are generated from the lights in boththe first and second wavelength bands, superposition of the lights intwo wavelength bands occurs.

Although in this state, independently acquiring optical intensitysignals based on phase differences of the first and second wavelengthbands is impossible, instead, signals from pixels include a componentthat corresponds to a case where a phase difference of lights incidenton a pair of incident regions adjacent to each other is observed with anequivalent wavelength. A fifth computation unit 1104 extracts thecomponent that corresponds to the case where the observation isperformed with the equivalent wavelength and calculates equivalent phasedifference information 119. The fifth computation unit 1104 is anexample of the computation circuitry.

Since such a configuration needs no switching of illuminations in timedivision, a photodetection device that is still simpler in configurationcan be achieved.

First Example

A first example of the present disclosure is described below.

In the present example, the first incident regions 104 and the secondincident regions 105 are arranged as illustrated in FIG. 4C. That is, inthe interference element 106, the first incident regions and the secondincident regions are alternately arranged on a column-by-column basis.In other words, the light in the first wavelength band, which has acenter wavelength referred to as λ₁, and the light in the secondwavelength band, which has a center wavelength referred to as λ₂, arealternately incident on the interference element 106 on acolumn-by-column basis. In each column, the incident regions and thelight shielding regions are alternately arranged.

The first pixels 110, the second pixels 111, the third pixels 112, andthe fourth pixels 113 are arranged as illustrated in FIG. 7C. Asdescribed above, the first and second pixels and the first incidentregions, and the third and fourth pixels and the second incident regionsare related to each other, respectively. The number of pixels is set tobe 100 pixels×100 pixels.

FIG. 12 illustrates a specific cross-sectional configuration of theinterference element 106 used in the present example. The interferenceelement 106 includes an optical coupling layer. The incident lightirradiates incident regions 1201 and light shielding regions 501. Alight shielding layer 1202 is arranged so as to distinguish the incidentregions and the light shielding regions from each other. The material ofthe light shielding layer is Al and the thickness of the light shieldinglayer is 100 nm. Each of the widths of the incident region and the lightshielding regions is 5.6 μm.

An optical coupling layer 502 is made up of six waveguide layers andgratings are formed on vertical interfaces of the waveguide layers. Thewaveguide layers are each a layer with a relatively high refractiveindex and in the present example, configured using Ta₂O₅. A material forsandwiching the waveguide layers is a transparent layer with arelatively low refractive index and in the present example, isconfigured using SiO₂. The depth of a grating is 0.2 μm and each pitchof the grating, which is indicated as A in FIG. 12, is 0.45 μm. Thethickness of a Ta₂O₅ layer, which is indicated as t₁ in FIG. 12, is 0.34μm, and the thickness of a SiO₂ layer between the waveguide layers,which is indicated as t₂ in FIG. 12, is 0.22 μm.

When light with a wavelength of 850 nm is caused to be perpendicularlyincident on the incident face of the interference element 106 configuredas described above, the intensity of the interference light 107 emittedfrom an interference light region 1203 and the intensity of thetransmitted light 108 emitted from a transmitted light region 1204 arecalculated by the Finite-difference time-domain method (FDTD). Asparameters of the incident light, the intensities of the lights incidenton the incident regions 1201 adjacent to each other are equalized and aphase difference is caused to vary from −180 degrees to 180 degrees.

FIG. 13 illustrates results of calculating the intensities of theinterference light 107 and the transmitted light 108 with respect to aphase difference of the incident light, and in FIG. 13, the degrees of aphase difference as a unit is denoted as [deg]. The intensity ratioindicates the ratio to the intensity of the incident light.

When the phase difference is approximately 0 degrees, that is, in phase,the intensity of the interference light is the highest and the intensityof the transmitted light is the lowest. When the phase difference isapproximately ±180 degrees, the intensity of the interference light isthe lowest and the intensity of the transmitted light is the highest.These results demonstrate that the intensities of the interference lightand the transmitted light vary, depending on a phase difference. Thisindicates that the interference light and the transmitted light areemitted as a result of mutual interference of lights incident fromadjacent incident regions in the interference element.

Described next is a procedure of estimating the shape of a measuredobject using this result on the basis of the light that has passedthrough the object.

A sample with the shape illustrated in FIG. 14A is set as the measuredobject. The sample is constituted of a bottom portion shaped like anarrow wedge and a central projecting portion. FIG. 14B schematicallyillustrates the shape of the sample viewed in the x direction. The wedgehas a thickness of 600 nm and the projecting portion has a height of 50μm. The refractive index of the sample is 1.45.

In the state where light incident from the bottom face side of thesample passes through the sample and an optical path length differenceis caused, the light is assumed to be incident on the optical system asthe incident light. It is further assumed that the light that has passedthrough the region corresponding to the plane in the range where x ofthe sample=1 to 100 and y of the sample=1 to 100 is incident on thepixels in the range of 100×100 pixels of the image sensor.

The center wavelengths of the lights caused to be incident on the sampleare λ₁=845 nm and λ₂=855 nm. The bandwidth of each light is 5 nm in fullwidth at half maximum.

FIGS. 15A to 15D each illustrate the intensity of the light incident oneach pixel of the image sensor. FIG. 15A depicts the interference lightwith the center wavelength λ₁, that is, the light incident on firstpixels, FIG. 15B depicts the interference light with the centerwavelength λ₂, that is, the light incident on second pixels, FIG. 15Cdepicts the transmitted light with the center wavelength λ₁, that is,the light incident on second pixels, and FIG. 15D depicts thetransmitted light with the center wavelength λ₂, that is, the lightincident on fourth pixels. In each of FIGS. 15A to 15D, the intensitiesof the pixels that do not correspond to the illustrated pixels, whichare for example the second, third, and fourth pixels in FIG. 15A, areindicated as being zero. Each of FIGS. 15A to 15D demonstrates that,when viewed in the column direction, that is, in the y direction of thedrawing, large variations in intensity are caused at locations where anoptical path length difference largely varies in adjacent incidentregions.

In actual measurements, when the relation illustrated in FIG. 13 isused, on the basis of the intensity of the light incident on each pixelof the image sensor, the absolute value of the phase difference at thepixel can be determined. This corresponds to the procedure ofdetermining the phase difference information through the computation inthe first computation unit 114 and the second computation unit 115.Since the phase difference value of the center wavelength λ₁ and thephase difference value of the center wavelength λ₂ are alternatelyobtained on a column-by-column basis, regarding a column for which theabsolute value of the phase difference with each center wavelengthcannot be obtained, the absolute value of the phase difference isdetermined through for example, interpolation using the absolute valuesof the phase difference of both nearest neighbor columns. FIGS. 16A and16B each illustrate the absolute values of the phase difference at thecenter wavelengths λ₁ and λ₂, which are calculated in this manner.

To discriminate the polarity of the phase difference, for example, thevariations in the absolute value of the phase difference may be observedat the time of inclining the sample while the x direction serves as anaxis. This is because the direction in which the absolute value of thephase difference increases or decreases varies, depending on thepolarity of the phase difference. FIGS. 17A and 17B each illustrate thevalues of the phase difference at the center wavelengths λ₁ and λ₂,which are determined together with the polarity in this manner.

Calculating the values of the phase difference of adjacent incidentregions at the equivalent wavelength λ_(eff) on the basis of the valuesof the phase difference of the adjacent incident regions at the centerwavelengths λ₁ and λ₂ is enabled by using the method described in forexample, Japanese Unexamined Patent Application Publication No.10-221032 or Yeou-Yen Cheng and James C. Wyant: “Two-wavelength phaseshifting interferometry”, Applied Optics, vol. 23, No. 24, pp. 4539 to4543. This corresponds to the procedure of determining the phasedifference information through the computation in the third computationunit 118. FIG. 18 illustrates the phase difference values at theequivalent wavelength λ_(eff), which are determined in this manner.

When the phase difference values at λ_(eff) are integrated in the columndirection, the phase values at λ_(eff) can be calculated. FIG. 19illustrates the calculation results of the phase values at λ_(eff).

The phase values at λ₁ and λ₂ may be determined by integrating the phasedifference values at λ₁ and λ₂ in the respective column directions andthen the phase values at λ_(eff) may be determined using the calculationresults. FIGS. 20A and 20B each illustrate the phase values at λ₁ andλ₂.

Since the distribution of optical path length differences can bedetermined on the basis of the phase values at λ_(eff), the shape of thesample can be reconstructed and estimated using the refractive indexvalues of the sample. FIG. 21 illustrates the estimated shape. It isdemonstrated that the original shape of the sample illustrated in FIG.14A can be reconstructed almost perfectly.

The shape with a step that has a height of approximately 50 μm like thepresent sample can be correctly reconstructed since the lights with twowavelengths of λ₁ and λ₂ are used. The equivalent wavelength λ_(eff)according to the present example is expressed as(855×845)/(855−845)=72.2 μm and thus, correct reconstruction can beperformed when the step complies with an optical path length differencethat does not exceed this equivalent wavelength. For comparison, FIGS.22A and 22B illustrate results of reconstructing the shape only from thelight of λ₁ or λ₂. It is demonstrated that since the step of theprojecting portion of the sample exceeds the wavelength, the shape isnot reconstructed precisely.

As described above, the present disclosure provides a photodetectiondevice that has an optical part smaller in size, is less susceptible tothe influence of an ambient environment, and can correctly measure theshape of an object even when the object includes a step beyond thewavelength of light.

Second Example

A second example of the present disclosure is described below.

The present example describes a method of measuring a step in a measuredobject using the photodetection device described in the third embodimentof the present disclosure.

The photodetection device employs the configuration illustrated in FIG.11. That is, the configuration where lights in the first and secondwavelength bands are not separated by the optical system in terms ofspace. The configuration of the interference element is similar to thatin the first example. As for the center wavelengths of the lights causedto be incident on the sample, similar to the first embodiment, λ₁=845 nmand λ₂=855 nm.

The samples that are shaped as illustrated in FIG. 23 are assumed as ameasured object. The two samples with different heights are caused to bein contact with each other and arranged while a step between the samplesis referred to as L. The refractive index of the samples is 1.45.

In the state where light incident from the bottom face side of thesamples passes through the samples and an optical path length differenceis caused by the step, the light is incident on the optical system asthe incident light.

FIGS. 24A and 24B each illustrate the intensities of the interferencelight and the transmitted light that are obtained when the lightincident on a pair of adjacent incident regions has this optical pathlength difference. The intensity ratio indicates the ratio of theintensity of the interference light or the transmitted light to theincident light. The intensity ratio is plotted while the step L servesas a parameter and the center wavelengths λ₁ and λ₂ are separate. Sincethe wavelengths of λ₁ and λ₂ are different from each other, a phasedifference deviates even when the step L remains identical. As a result,the intensities of the interference light and the transmitted lightdeviate between λ₁ and λ₂ in intensity, depending on the step L.

Since in the configuration of the photodetection device illustrated inFIG. 11, the lights with the center wavelengths λ₁ and λ₂ are incidentsimultaneously on the pixels of the image sensor, an optical intensitysignal that can be obtained from the image sensor is a result of thesuperposition of the lights with λ₁ and λ₂. FIGS. 25A and 25B illustraterespective plots of the relations between the intensities of thesuperposed interference light and the transmitted light and the step L.As demonstrated in FIGS. 25A and 25B, regarding both the interferencelight and the transmitted light, a component of an envelope variesgently with respect to the step L. This is the component thatcorresponds to the case where a phase difference is observed at theequivalent wavelength λ_(eff).

When this phenomenon is used, for example, a sample is caused to undergothermal expansion and variations in the step L can be measured. That is,when the intensity of the interference light or the transmitted light isobserved while varying the step L and a component of an envelope isextracted as in the procedure that corresponds to the computation in thefifth computation unit, a step beyond the wavelength of the incidentlight can be correctly measured.

Although in each photodetection device according to the above-describedembodiments, the incident light is described as lights in two bands withdifferent center wavelengths, the number of bands may be three or more.The value of a wavelength is not limited to the values mentioned aboveand may be set so as to be most suitable for a purpose.

The configurations of the photodetection device used in theabove-described embodiments and examples are not limited to thosedescribed above and can be changed to suitable configurations within arange where the above-described configurations and advantages of thepresent disclosure are satisfied.

In the present disclosure, all or part of the group consisting of thefirst computation unit 114, the second computation unit 115, the thirdcomputation unit 118, the fourth computation unit 1009, and fifthcomputation unit 1104 may be implemented as one or more of electroniccircuits including, but not limited to, a semiconductor device, asemiconductor integrated circuit (IC) or an LSI. The LSI or IC can beintegrated into one chip, or also can be a combination of plural chips.For example, functional blocks other than a memory may be integratedinto one chip. The name used here is LSI or IC, but it may also becalled system LSI, VLSI (very large scale integration), or ULSI (ultralarge scale integration) depending on the degree of integration. A FieldProgrammable Gate Array (FPGA) that can be programmed aftermanufacturing an LSI or a reconfigurable logic device that allowsreconfiguration of the connection or setup of circuit cells inside theLSI can be used for the same purpose.

Further, it is also possible that all or part of the group isimplemented by executing software. In such a case, the software isrecorded on one or more non-transitory recording media such as a ROM, anoptical disk or a hard disk drive, and when the software is executed bya processor, the software causes the processor together with peripheraldevices to execute the functions specified in the software. A system orapparatus may include such one or more non-transitory recording media onwhich the software is recorded and a processor together with necessaryhardware devices such as an interface.

The photodetection device according to the present disclosure isapplicable to measurements for industrial, medical, cosmetic, security,and on-vehicle purposes or the like. Further, the photodetection deviceaccording to the present disclosure enables new imaging functions suchas phase difference distribution or phase distribution to be added tofor example, digital still cameras or video cameras.

What is claimed is:
 1. A photodetection device comprising: an imagesensor that includes first pixels, second pixels, third pixels, andfourth pixels; an interference element that includes first incidentregions and second incident regions; and an optical system that causeslight in a first wavelength band to be incident on the first incidentregions and causes light in a second wavelength band different from thefirst wavelength band to be incident on the second incident regions,wherein the interference element causes first interference of part ofthe light in the first wavelength band incident on two first incidentregions that are included in the first incident regions and that areadjacent to each other, and guides resultant light of the firstinterference to any of the first pixels and guides another part of thelight in the first wavelength band incident on the two first incidentregions to any of the second pixels, and causes second interference ofpart of the light in the second wavelength band incident on two secondincident regions that are included in the second incident regions andthat are adjacent to each other, and guides resultant light of thesecond interference to any of the third pixels, and guides another partof the light in the second wavelength band incident on the two secondincident regions to any of the fourth pixels.
 2. The photodetectiondevice according to claim 1, further comprising: computation circuitrythat determines first phase difference information using opticalintensity information detected at the first pixels and optical intensityinformation detected at the second pixels, and determines second phasedifference information using optical intensity information detected atthe third pixels and optical intensity information detected at thefourth pixels.
 3. The photodetection device according to claim 2,wherein the computation circuitry determines phase differenceinformation at an equivalent wavelength of a first wavelength includedin the first wavelength band and a second wavelength included in thesecond wavelength band using the first phase difference information andthe second phase difference information.
 4. The photodetection deviceaccording to claim 1, wherein the interference element includes opticalcoupling layers, and the optical coupling layers each include awaveguide layer that includes a diffraction grating.
 5. Thephotodetection device according to claim 4, wherein the interferenceelement includes a first light shielding region positioned between thetwo first incident regions and a second light shielding regionpositioned between the two second incident regions, the optical couplinglayers include an optical coupling layer positioned at a locationcorresponding to the two first incident regions and the first lightshielding region, or the two second incident regions and the secondlight shielding region, the second pixels include two second pixelspositioned at a location corresponding to the two first incidentregions, the first pixels include a first pixel positioned at a locationcorresponding to the first light shielding region, the fourth pixelsinclude two fourth pixels positioned at a location corresponding to thetwo second incident regions, and the third pixels include a third pixelpositioned at a location corresponding to the second light shieldingregion.
 6. The photodetection device according to claim 1, wherein theinterference element includes a first optical propagation path, a secondoptical propagation path, and a third optical propagation path coupledbetween the first optical propagation path and the second opticalpropagation path.
 7. The photodetection device according to claim 6,wherein the first optical propagation path includes an incident portionon which light from one of the two first incident regions or one of thetwo second incident regions is incident, and an emission portion fromwhich part of the light that is incident is emitted to any of the secondpixels or any of the fourth pixels, and the second optical propagationpath includes an incident portion on which light from the other of thetwo first incident regions or the other of the two second incidentregions is incident, and an emission portion from which part of thelight that is incident is emitted to any of the second pixels or any ofthe fourth pixels.
 8. The photodetection device according to claim 7,wherein the interference element further includes a fourth opticalpropagation path, and the fourth optical propagation path includes anincident portion coupled to the third optical propagation path, and anemission portion from which the light incident from the incident portionis emitted to any of the first pixels or any of the third pixels.
 9. Thephotodetection device according to claim 8, wherein the first opticalpropagation path, the second optical propagation path, the third opticalpropagation path, and the fourth optical propagation path are configuredwith a photonic crystal.
 10. The photodetection device according toclaim 6, wherein the first optical propagation path, the second opticalpropagation path, and the third optical propagation path are configuredwith a photonic crystal.
 11. The photodetection device according toclaim 1, wherein the optical system includes a filter array thatincludes first bandpass filters that selectively transmit the light inthe first wavelength band, and second bandpass filters that selectivelytransmit the light in the second wavelength band.
 12. The photodetectiondevice according to claim 1, wherein the optical system includes a firstbandpass filter that selectively transmits the light in the firstwavelength band, a second bandpass filter that selectively transmits thelight in the second wavelength band, and an array-shaped optical elementthat causes the light in the first wavelength band transmitted throughthe first bandpass filter to be incident on the first incident regions,and causes the light in the second wavelength band transmitted throughthe second bandpass filter to be incident on the second incidentregions.